Shopping for a new mill.

Shopping for a new mill.

Deus Machina
Deus Machina

August 1st, 2011, 4:19 am #1

It's coming up time to upgrade from my mini machines. Doing anything the size of a gun body has become tedious, and I want something large enough to swing a flycutter.

The problem: I'm still in an apartment with a rented garage and can't rewire. So I'm still stuck on 110 power with--I assume--a 15A breaker.

So, I've been trying to narrow it down to Grizzly's G0463 http://www.grizzly.com/products/Mill-Drill/G0463 or G0619 http://www.grizzly.com/products/6-x-21-Mill-Drill/G0619 The latter is more expensive, but has a spindle depth readout, tilting head, tachometer, tilting head, and another 1/4HP. I've never used--or really needed--a tach before.

All nice, but I would add a spindle depth readout anyway, and I'm not sure that I would use the tilting head instead of, say, 45* cutters and/or a tilting vice.

I'm also looking at the G0704 http://www.grizzly.com/products/Drill-M ... tand/G0704 , because it's less expensive and comes with a spindle depth readout and free stand, on the tradeoff of less mass and a shorter vertical envelope but larger horizontal.

Reviews have people that either like the odd Z-axis handle or find it inconvenient, and some skeptical that the 3.2A motor actually produces a full horse.

So... Anyone with experience with these, or at least with the varying features on other mills, that I might never use or wish I had later?

I really do want a rewired Bridgeport or the G3102 http://www.grizzly.com/products/Vertical-Mill/G3102 , but can't really spring $3k and something that trips my breaker would be useless, since I can't change it at all.
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Russ Kepler
Russ Kepler

August 1st, 2011, 1:34 pm #2

1 HP is 750 watts (give or take) so a motor using 3.2A at 120V isn't generating even a single HP, more like .5HP at 100% efficiency (and that's not happening).

120V at 15A is 2.4 HP, so that's the max load you can handle. Since there are VFDs that take 120 in and spit 240 3 phase out that's also an option (albeit a little pricey), so something like a nice Clausing, Rockwell or smaller Bridgeport are options, even a used Enco RF30 . Keep looking around, I picked up a nice Hardinge horizontal with a vertical head (and full set of tooling) for something like $750 a year or so back and there's not a lot of stuff you couldn't do with that rig.

Looking at it the G3102 likely wouldn't trip your breaker. If it were 3 phase and you used a VFD you could be sure, the slow start on a VFD is a lot easier on breakers than the surge from a direct connection.

But in summary I'd suggest getting as much mill as you can - you may not always need all of the travel but not having it when needed can hurt.
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sniper1rfa
sniper1rfa

August 1st, 2011, 8:26 pm #3

Maybe 1, but definitely not 2.4.

Remember that AC power is not as simple as DC power - amps*volts doesn't work for AC.
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Uticus
Uticus

August 1st, 2011, 11:50 pm #4

You'd be pushing the limits of the breaker, but if he was running a drive it largely eliminates the power factor issue. Ramp up slowly on start-up and you can probably run a 2HP motor.

Also 2.4Hp is not a standard motor size, so it would be hard to find this regardless
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sniper1rfa
sniper1rfa

August 2nd, 2011, 1:22 am #5

sounds sketchy to me. Baldor lists their 2HP motors at 23 amps on 115VAC. 2.5 would be

I think 1.5HP is about as much as I'd bother trying.
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Uticus
Uticus

August 2nd, 2011, 1:42 am #6

I was ignoring the magnetizing current when I was running the numbers. I'm used to much larger motors that 2HP where the magnetizing current is a much lower percentage of motor full load amp. (The last motor I was involved in sizing at work ended up being a 400HP motor custom ordered with a core from a much larger motor for a starting a high inertia load.)
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Russ Kepler
Russ Kepler

August 2nd, 2011, 2:20 pm #7

Maybe 1, but definitely not 2.4.

Remember that AC power is not as simple as DC power - amps*volts doesn't work for AC.
Watts works for RMS voltage, AC, DC square wave or triangular wave. Where the calculated power fails to match motor 'power' is in a couple of areas:

1) Surge power on start. VFDs can be set to ramp up and minimize the surge that a directly connected motor will give.

2) Motor efficiency - most motors are below 100%, most in the range of 80% in the size that we're talking about.

So a 2HP 120V single phase VFD rated at 2HP out at 240V 3 phase could run a 2HP motor while drawing right at the 15A limit when the motor is under max stress, most of the time draw would be a lot less. It's right at the top end of what you can do with the 15A wall socket, and I'd really feel more comfortable if you were using a utility outlet (20A) rather than a convenience outlet (15A) just for the headroom. But you could run a 2HP mill off the 15A 120V outlet.

If I were doing this I'd just pull a big-ass extension cord from the electric dryer outlet, or put a non-code pigtail from the electric over or range breaker to an additional outlet - something I could pull from the box when I had to.

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